HTML Twins

#1 01-05-2006, 04:24 PM

I am no JavaScript progammer, and unfortunately am having to babysit an
old code base that has a lot of JavaScript in it.

I have two questions:

(1) Can two HTML controls have the same name? It looks like the obvious
answer is NO.

(2) What if? What if the developer has given two HTML controls the same
name, i.e has created the same button more than once with exactly the
same name and all other attributes? What happens then?

Ok, before you call me lazy, let me tell you, I tried it. Here's what I
did on a spike solution.

<HTML>

<SCRIPT>
function doFoo()
{
document.forms[0].edt.disabled=!document.forms[0].edt.disabled;
}
</SCRIPT>

<FORM name="frmFoo">
<INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
<INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
</FORM>

</HTML>

Like I expected, clicking any of the buttons did not disable either of
them.

So, I wanted to do something like this:

For Each HTML Control In The Form On The Document
If The HTML Control Has a Value Of Edit Then
Disable It, or do something with it like show me its name and
value
End If
Next HTML Control

So, here's what I did:

<HTML>

<SCRIPT>

function doFoo()
{
alert(document.forms[0].children.length)
for(i=0; i<=document.forms[0].children.length-1; i++)
{
alert(document.forms[0].children[i].name)
if (document.forms[0].children[i].value == 'Edit')
document.forms[0].children[i].disabled=false;
}
}

</SCRIPT>

<FORM name="frmFoo">
<INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
<INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
</FORM>

</HTML>

And lo! as I expected, the form has just one element reference that is
valid and the other as an invalid reference.

Given this situation on my "actual" code that I am babysitting (someone
else wrote it), and it is HUGE, and it has all JavaScript and HTML
elements dynamically generated from ASP code and some strong glue by
way of screwed up logic, what options do I have other than re-write the
page?

I am running IE 6 on Win 2000, if that is relevant.

#2 01-05-2006, 04:24 PM

Sathyaish wrote:
> (1) Can two HTML controls have the same name? It looks like the
> obvious answer is NO.

Yes they can. In fact, it's required for radio button groups!

> (2) What if? What if the developer has given two HTML controls the
> same name, i.e has created the same button more than once with
> exactly the same name and all other attributes? What happens then?

Instead of document.forms['formName'].elements['elementName'] referring to a
single input, it will now be a reference to a collection of the inputs with
form name 'elementName'. In fact, the elements with the same name don't even
need to be of the same type!

> For Each HTML Control In The Form On The Document
> If The HTML Control Has a Value Of Edit Then
> Disable It, or do something with it like show me its name and
> value
> End If
> Next HTML Control

var inputs = document.forms['formName'].elements;
for (var i=0; i<inputs.length; i++) {
if (inputs[i].value && inputs[i].value=='Edit') {
inputs[i].dislabed = true;
}
}

Although, wouldn't you want to check for the NAME attribute rather than
VALUE?

--
Matt Kruse
http://www.JavascriptToolbox.com
http://www.AjaxToolbox.com

#3 01-05-2006, 04:24 PM

Sathyaish wrote:
> I am no JavaScript progammer, and unfortunately am having to babysit an
> old code base that has a lot of JavaScript in it.
>
> I have two questions:
>
> (1) Can two HTML controls have the same name? It looks like the obvious
> answer is NO.

The answer is YES. Creating form elements with the same name creates an
array...

a very simple example may demonstrate:

<script type="text/javascript">
function tally(form){
var prices=form.price;
var sum=0;
for(var i=0; i<prices.length; i++){
sum+=parseFloat(prices[i].value);
}
form.subtotal.value=sum;
}
</script>

<form>
1:<input type="text" name="price" value="1.50"><br>
2:<input type="text" name="price" value="2.70"><br>
3:<input type="text" name="price" value="45.00"><br>
4:<input type="text" name="price" value="4.55"><br>
5:<input type="text" name="price" value="2.09"><br>
<hr>
<input type="text" name="subtotal" size"5"><br>
<input type="button" onclick="tally(this.form)" value="Subtotal">
</form>

> (2) What if? What if the developer has given two HTML controls the same
> name, i.e has created the same button more than once with exactly the
> same name and all other attributes? What happens then?
>
> Ok, before you call me lazy, let me tell you, I tried it. Here's what I
> did on a spike solution.
>
>
> <HTML>
>
> <SCRIPT>
> function doFoo()
> {
> document.forms[0].edt.disabled=!document.forms[0].edt.disabled;
> }
> </SCRIPT>
>
> <FORM name="frmFoo">
> <INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
> <INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
> </FORM>
>
> </HTML>
>

They would do the same thing, just like having a duplicate function
buttons say at the top of the page and at the bottom for convenience

<snip>

--
Take care,

Jonathan
-------------------
LITTLE WORKS STUDIO
http://www.LittleWorksStudio.com

#4 01-05-2006, 04:24 PM

> (1) Can two HTML controls have the same name? It looks like the obvious
> answer is NO.

Yes they can, for instance, two radio buttons can (should) have the same NAME but
they must (should) have a unique ID.

> (2) What if? What if the developer has given two HTML controls the same
> name, i.e has created the same button more than once with exactly the
> same name and all other attributes? What happens then?

The NAME is only used when a FORM and its child controls are sent back to the
server. The server identifies each control thru its NAME. If the server is not
interested in the value(s) of the controls with the same name, then it does not
matter.

JavaScript on the client-side though typically uses the ID (which should be
unique), but if an ID is not specified, then it will use the NAME.

Brian

#5 01-05-2006, 04:24 PM

Sathyaish wrote:

> (1) Can two HTML controls have the same name? It looks like the obvious
> answer is NO.

No, the answer is YES, of course! For example, there would be no way
to implement radio buttons if it was NO.

> (2) What if? What if the developer has given two HTML controls the same
> name, i.e has created the same button more than once with exactly the
> same name and all other attributes? What happens then?

Then all controls with the same name, as all elements with the same
name, become part of a NodeList collection where each element can be
referred to by zero-based index.

> [...]
> <HTML>
>
> <SCRIPT>

That is not Valid (X)HTML. <URL:http://validator.w3.org/>

> function doFoo()
> {
> document.forms[0].edt.disabled=!document.forms[0].edt.disabled;

Should be at least

var es = document.forms[0].elements, edt0;
if (((edt0 = es['edt'][0]).disabled = !es['edt'][1].disabled))
{
edt0.disabled = !es['edt'][1].disabled ? "disabled" : "";
}

> }
> </SCRIPT>
>
> <FORM name="frmFoo">
> <INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
> <INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
> </FORM>

It is not necessary to refer to the form by index/name or to the event
target by name. Use `this' within intrinsic event handler attribute
values to refer to the event target and use `this.form' (or the
equivalent in the called method) to refer to the ancestor `form'
element.

> Like I expected, clicking any of the buttons did not disable either of
> them.

Because you referred to the wrong object. The same-named elements were in a
collection, and the collection itself had no `disabled' property before you
added one. Of course the user-defined property, if it was even created,
did not change presentation of the respective elements.

> So, I wanted to do something like this:
>
>
> For Each HTML Control In The Form On The Document
> If The HTML Control Has a Value Of Edit Then
> Disable It, or do something with it like show me its name and
> value
> End If
> Next HTML Control

// For Each HTML Control In The Form On The Document
var f = referenceToFormOnTheDocument;
for (var es = f.elements, i = es.length; i--

{
var e = es[i];

if (e.value == "Edit")
{
// Disable It,
if ((e.disabled = false))
{
e.disabled = "disabled";
}

// or do something with it like show me its name and value
alert([e.name, " = ", e.value].join(""));

// End If
}
// Next HTML Control
}

> [...]
> <HTML>
>
> <SCRIPT>

That's not Valid (X)HTML either.

> function doFoo()
> {
> alert(document.forms[0].children.length)

`children' is a non-standard property of the IE-DOM. You are looking for
the both standards compliant and downwards compatible `elements' property
instead which includes all form controls, rather than the standard
equivalent to `children' of `childNodes' which would include all child
elements as well.

> for(i=0; i<=document.forms[0].children.length-1; i++)

for (var i = 0, len = document.forms[0].children.length; i < len; i++)

> {
> alert(document.forms[0].children[i].name)
> if (document.forms[0].children[i].value == 'Edit')
> document.forms[0].children[i].disabled=false;
> }
> }
>
> </SCRIPT>
>
> <FORM name="frmFoo">
> <INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
> <INPUT type="button" value="Edit" name="edt" onClick="return doFoo()"/>
^[1]
> </FORM>
>
> </HTML>
>
>
> And lo! as I expected, the form has just one element reference that is
> valid and the other as an invalid reference.

That is probably because you referred to all the child nodes of
the element instead of to all form control child element nodes.

> [...]
> I am running IE 6 on Win 2000, if that is relevant.

Yes, IE does not support XHTML.[1]

<URL:http://hixie.ch/advocacy/xhtml>

HTH

PointedEars, X-Post & F'up2 comp.lang.javascript

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